The present invention relates to a polishing disc and a method of manufacturing the same. More specifically, the present invention relates to an improved polishing disc that is used by being mounted on a rotary tool such as a grinder or the like to grind and polish a material of steel, non-ferrous metal, stone, wood, ceramics and the like and to a method of manufacturing the same.
Disc type polishing grindstones are mounted on a grinding machine and rotated thereby to grind and to polish a workpiece composed of steel, non-ferrous metal, stone, wood, ceramics and the like, and used by being mounted on a rotary tool such as a grinder or the like. They are widely used in the various fields of industries such as building construction, shipbuilding, engineering works, electric works and the like.
An offset type resinoid grindstone disc, for example, is exemplified as a technology of a conventional grinding and polishing disc. This is a disc composed of a phenol grindstone formed in a disc shape and mainly used for grinding. A workpiece that can be ground thereby is limited only to a little hard material such as cast iron, stainless steel and the like.
The offset type resinoid grindstone disc has bad heat radiation on the grinding surface thereof because it is inferior in air permeability in grinding. Thus, the offset type resinoid grindstone disc has such a problem that burning is caused to a workpiece and that the ability of the disc is reduced because it wears by itself and is loaded with chips ground from the workpiece.
An offset type flexible grindstone disc is a thin disc composed of a glass net reinforced grindstone formed in a disc shape and can be widely applied to cutting, grinding, polishing and the like. The offset type flexible grindstone disc is preferably used in the grinding, polishing and the like of a flat surface because it is excellent in cushioning. However, the flexible grindstone disc has a problem in that it is promptly worn and consumed and loading is caused thereto and that a workpiece is burnt due to the insufficient radiation of the disc while it is used. Further, a material that can be polished and ground by the disc is limited only to steel, cast iron, and stainless steel.
Further, a sand paper type disc, which is constructed such that abrasive pieces each composed of a sand paper having abrasive grains coated on the surface thereof, are radially disposed while being partially stacked, has a similar problem. That is, a workpiece is prevented from being burnt by the good air permeability of the disc at the beginning of use thereof. However, exfoliated abrasive grains and the fiber pieces of the sand paper are sunk into the disc in a short period of time and the disc is loaded therewith, which reduces the ability of the disc as well as the air permeability thereof is deteriorated, and the workpiece is burned due to insufficient radiation. The disc can be used in a relatively wide range of a workpiece such as wood, steel, and stainless steel.
A problem that is commonly arisen in these polishing discs resides in that since they are used by being rotated at a very high speed with respect to a workpiece, the workpiece is burnt by frictional heat of high temperature generated thereby. A reason why this problem is arisen is that a large pressure is applied to the workpiece by the polishing disc when it is polished thereby. To solve this problem, it has been examined to compose the polishing disc of synthetic rubber to ease the contact of the polishing disc with the workpiece. However, since the synthetic rubber ordinarily has small pores, it is loaded with chips that are produced when the workpiece is polished and further it is exfoliated from a base sheet when it is rotated at a high speed because it is badly bonded thereto. Thus, the synthetic rubber cannot be practically used for a long period of time.
Japanese Utility Model Registration No. 3064081 proposes an idea for improving the defect of the synthetic resin. That is, it proposes a polishing disc composed of elastic synthetic resin sheets of urethane that are mixed with abrasive grains and disposed radially so as to form recessed portions. A workpiece is prevented from being burnt by the elasticity of the synthetic resin, and the radial disposition of the recessed portions makes airflow and the air cooling effect of which further prevents the burning of the workpiece by. In addition, a bonding property that withstands high speed rotation can be realized by a cloth held and bonded between the urethane synthetic resin and a base sheet.
However, while the polishing disc is not exfoliated from the base sheet when it is rotated at a high speed in a practical use, an effect of preventing the burning of a workpiece for a long period of time cannot be found because the recessed portions are collapsed and blocked due to the elasticity of the polishing disc. Thus, it cannot be said that the polishing disc has a practically usable ability because an air cooling effect that is realized by the maintenance of air permeability is exhibited for a very short period of time.
A flat disc with holes as shown in FIG. 3 that prevents loading in consideration of air permeability is known. The flat disc with holes 21 is a disc that polishes a workpiece by being mounted on a rotary tool through a shaft hole 24 and rotated at a high speed. The flat disc with holes 21 includes a flat abrasive member 26 formed on a ring portion 27, and ventilation holes 28 are formed through the abrasive member 26 at equal intervals. The ventilation holes 28 exhibit an effect of preventing burning by discharging polished chips and ground chips, maintain air permeability, and dissipating heat.
However, while the radiation property of the polishing disc is improved, the abrasive member 26 is composed of hard aluminum oxide, thus when a workpiece is composed of, for example, stainless steel, it is broken and flown into pieces when the disc is rotated at 5000 rpm or more. Accordingly, the polishing disc cannot be effectively used. Further, the disc has a problem that large noise and vibration are produced in polishing because the abrasive member 26 is hard. Furthermore, while the disc is protected by a pad attached to the back surface thereof for safety, the pad is liable to be broken because the ventilation holes 28 have a large diameter, which prevents the abrasive member 26 from being used until it is perfectly consumed. Thus, the disc is is ineffectively used and an operating cost is increased.
Further, recently, it is required to polish and grind many kinds of workpieces composed of various materials ranging from a very hard material such as cemented carbide, special stainless steel, and the like to a relatively soft material such as aluminum, copper, magnesium, and the like, in addition to that the workpieces have various characteristics. Hard workpieces are liable to be more burnt because they are heated to a high temperature, whereas soft workpieces are liable to cause loading on a disc because chips are produced therefrom in a large amount. In such circumstances, it has been desired to polish and grind a wide range of workpieces with polishing discs the number of which is as small as possible taking workability into consideration.
As described above, the conventional polishing discs have a problem that loading and burning are caused in a short period of time due to an insufficient cooling ability and the ability of the disc is reduced thereby and that loading and burning are further caused because the discs are heated to a high temperature due to insufficient radiation. Moreover, at present, it is required that no loading and burning are caused under the severe polishing and grinding conditions of ultra-high rotation in which a disc is rotated at least 10000 rpm for the improvement of a manufacturing efficiency. Accordingly, there is a large object to be achieved that the above problems must be improved under the above severe conditions with polishing discs the number of which is as small as possible in the polishing and grinding of workpieces the types of which are being further increased.
The inventors proposed an open type reticulated polishing disc and a manufacturing method of the same in Japanese Patent Application No. 2000-107606 to solve the above-mentioned conventional problems, and the present invention is obtained by further studying the above proposal. Accordingly, it is an object of the present invention to provide a soft polishing disc with holes that has a good air ventilation property, maintains an air cooling effect for a long period of time, is difficult to be loaded with chips, increases the heat radiation property of an abrasive surface and makes it to difficult for a workpiece to be burnt and that can stably grind and polish a workpiece even if it is rotated at an ultra-high rotational speed of 10000 rpm or more.
As a result of various examinations, the inventors have found that the above object can be achieved by providing a soft polishing disc with holes and a method of manufacturing the same, the soft polishing disc with holes being arranged such that an abrasive member is obtained by radially disposing abrasive pieces each composed of a sandpaper, on which abrasive grains are coated, on a flexible base cloth while partially stacking them and by coupling the abrasive pieces with each other through a thermosetting resin, and then ventilation holes are formed through the abrasive member.
That is, according to the present invention, there is provided a soft polishing disc with holes usable for grinding and polishing a workpiece, comprising:
a back sheet mounted on a rotary tool and rotated thereby, and
an abrasive member composed of abrasive pieces that are disposed radially on a ring portion having an outside diameter and an inside diameter from the center of the ring thereof and bonded to each other,
wherein each of the abrasive pieces is composed of a sand paper, a thermosetting resin is used as a coupling agent for bonding the abrasive pieces with each other, and a plurality of ventilation holes are formed through the abrasive member at predetermined intervals.
In the soft polishing disc with holes of the present invention, it is preferable that the grade of roughness of the sand paper be about #30 to #1000, and it is preferable that the base cloth of the sand paper be composed of cotton or paper which is soft and difficult to be melted by heat.
It is preferable that the thermosetting resin be melamine resin, silicon resin, phenol resin, urea resin that are cured by a polycondensation reaction and be epoxy resin, acrylic resin, etc. that are cured by a polyaddition reaction. It is preferable that the thermosetting resin is mixed with abrasive grains.
It is preferable that the ventilation holes formed through the above-mentioned have a diameter of about 3 to 5 mm and the intervals of adjacent ventilation holes be set to about 5 to 20 mm. Further, it is preferable that the ventilation holes pass through at least the abrasive member.
In the soft polishing disc with holes of the present invention, it is preferable that the abrasive pieces be radially disposed while being partially stacked so as to remain recessed portions.
It is preferable that the length of the lateral portion of each of the abrasive pieces, which are disposed around the circumference of the inside diameter of the ring portion, be xe2x85x9 to {fraction (1/12)} of the circumference of the inside diameter of the ring portion and that the length of the longitudinal portion of each of the abrasive pieces, which are disposed a long a radial direction of the ring portion, be longer than the radial length of the ring portion by about 0 to 3 mm.
It is preferable for the purpose of improving safety that the abrasive member be formed such that the lateral portions of the abrasive pieces are bonded along the tangential lines of the circumference of the inside diameter of the ring portion, that the longitudinal portions thereof be bonded in the radial directions of the ring portion as well as 3 to 10 abrasive pieces are stacked in the thickness direction of the ring portion and that the stacked portions of the abrasive pieces have an overlap width of about 1 to 5 mm.
It is preferable that the material of the back sheet be a glass fiber reinforced phenol laminated sheet having a napped or irregular surface so as to have an increased coupling force with the abrasive pieces. It is also preferable that the glass fiber reinforced phenol laminated sheet is mixed with abrasive grains so as to provide the back sheet with a polishing ability.
Further, according to the present invention, a method of manufacturing a soft polishing disc with holes usable for grinding and polishing a workpiece, comprising: a back sheet mounted on a rotary tool and rotated thereby, and an abrasive member composed of abrasive pieces that are disposed radially on a ring portion having an outside diameter and an inside diameter from the center of the ring thereof and bonded to each other; the method comprising the steps of:
disposing the abrasive pieces each composed of a sand paper together with a thermosetting resin held therebetween in a predetermined pattern while partially stacking them,
coupling the abrasive pieces with each other and hardening them for about 1 to 10 hours at a temperature of about 80 to 200xc2x0 C. at a pressure of about 10 to 100 kgf/cm3, and
laminating and bonding the abrasive pieces to the back sheet and forming ventilation holes through at least the abrasive pieces. It is also preferable that the thermosetting resin be mixed with abrasive grains.
Further, it is preferable that the abrasive pieces be bonded to the back sheet by being baked using a one liquid type epoxy resin for 3 hours at a temperature of about 80xc2x0 C.